大肠埃希菌对氟喹诺酮类药物耐药机制的研究进展

大肠埃希菌是革兰阴性杆菌感染最常见的病原菌之一，据报道，全球每年因感染产毒素性大肠埃希菌而发病的患者达6．5亿，并造成超过80万5岁以下儿童死亡，我国不少地区大肠埃希菌在腹泻病人的病原谱中占首位［1］。氟喹诺酮类药物是治疗大肠埃希菌感染的主要抗菌药物，在20世纪80年代及90年代初大肠埃希菌中几乎没有耐氟喹诺酮类药物的菌株，但随着氟喹诺酮类（ FQNS）的广泛使用，2004至2005年度卫生部全国细菌耐药监测网监测结果显示，大肠埃希菌对环丙沙星、左氧氟沙星的耐药率分别为64．9％、56．7％；2011至2012年度卫生部全国细菌耐药监测网监测结果显示，大肠埃希菌对环丙沙星、左氧氟沙星的耐药率分别为65．7％、61．6％。在我国临床分离大肠埃希菌对FQNS的耐药率处于全球前列。大肠埃希菌对氟喹诺酮类药物的耐药机制主要为染色体介导和质粒介导［1］，包括：（1）编码 DNA 解旋酶（DNA gy－rase）和拓扑异构酶Ⅳ（ topoisomerase Ⅳ，Topo Ⅳ）靶酶的基因发生突变，降低了与氟喹诺酮类药物的亲和力而耐药；（2）通过外排泵使抗菌药物外排增加，同时使被排出的药物不易再透过外膜进入菌体，从而降低药物在菌体内蓄积；（3）细胞膜通透性改变，膜孔蛋白缺失或低表达，降低了水溶性抗菌药物的透过，使细菌产生耐药；（4）大肠埃希菌多重耐药基因机制；（5）质粒编码的氟喹诺酮类耐药基因qnr、aac （6’）－Ib－er及qe－pA基因［2］。

Reversal mechanism of arsenic trioxide in the drug resistance of human gastric cancer cell line SGC7901/ADR

Objective： To investigate the reversal effect of arsenic trioxide （As2O3） on the multidrug resistance of human gastric tumor SGC7901/ADR cell line to adriamycin （ADM） and its reversal mechanisms, Methods： The non-cytotoxic concentration of As2O3 and the sensitivity of SGC7901/ADR cells toADM were detected by MTT assay, The drug concentration and P-gp function of SGC7901/ADR cells were measured with flow cytometry （FCM）, and the impacts of As2O3 on the GST-Π and Topo Ⅱ expressions of SGC7901/ADR cells were analyzed by immunohistochemical method. Results： As2O3 at 0,4 to 0.8 μmol/L concentrations were not significantly cytotoxic to SGC7901/ADR cells, As2O3 at 0.8 μmol/L could improve the sensitivity of SGC7901/ADR cells to ADM via inhibiting P-gp function, down-regulating GST-Π expression and increasing the intracellular accumulation of ADM in SGC7901/ADR cells. Conclusion： As2O3 can reverse partly the drug-resistance of SGC7901/ADR cells to ADM, which may be related with inhibiting the P-gp function and down-regulating GST-Π expression.

Epigenetic regulation mechanism of ABCG2 induced drug-resistant phenotype

The aim of this study is to investigate epigenetic mechanism of ABCG2 induced drug-resistance. It is not only expatiate for drug-resistance regulation mechanism in all-round, but also to provide scientific experimental basis for selecting target to reverse its drug-resistance. Apply methylation-specific PCR （MSP） to have tested methylation of ABCG2 promoter region -359 to -353 specific positions in breast cancer tissues and paired adjacent tissue of 22 cases and test their methylation positions with MSP products for sequencing; and adopt fluorescent quantitation RT-PCR to test expression level DNMT1, DNMT3A, DNMT3B and ABCG2; to make analysis on relationship between them with statistical spearman correlation. Specific positions of ABCG2 gene promoter region of 18 cases among the 22 cases with breast cancer （18/22, 82%） existed high methylation （P〈0.05）, MSP products sequencing proved methylation of the specific position, and mRNA expression level was relative higher in remarkable positive correlation （P〈0.05） ABCG2, DNMT1, DNMT3A, DNMT3B mRNA expression levels in breast cancer tissues were obviously higher than adjacent tissues （P〈0.01）, and DNMT3B expression level was obviously higher than DNMT1 and DNMT3A （P〈0.01） in negative correlation with ABCG2 gene expression （P=0.001）. -359 to -353 positions of promoter regions of ABCG2gene existed high methylation capable to push expression of this gene in beast cancer tissue. DNMT3B is involved in expression regulation in ABCG2 gene, and provides new scientific basis for drug-resistance target as reverse ABCG2 induction

Effect of Different Bioassay Methods on Enzymatic Characteristics of Cotton Aphid, Aphis gossypfi Glover （Hemiptera：Aphididae）

In this study, the susceptibility of three populations of cotton aphid, Aph＆ gossypii Glover （Hemiptera：Aphididae） was assayed to imidacloprid （35SC） and thiametoxam （50WG）. The involvement of metabolic enzymes in the resistance strain of cotton aphid to the neonicotinoids was determined by the biochemical biomarkers and the resistance mechanism was determined as CaE. In another study, three different bioassay experiments were designed for detecting the susceptibility of cotton aphid to imidacloprid and thiametoxam and the effect of these two insecticides on the enzymatic activity of cotton aphid was assessed in the adult aphids treated with three different bioassay methods using a modified version of the FAO dip test, residue bioassay procedure and starvation method. Our findings suggested that the type of bioassay methods is very important when aphids＇ populations assess for the resistance against the neonicotinod insecticides. It has shown the starvation method is the most reliable method compared with other methods.

Discussion on research methods of bacterial resistant mutation mechanisms under selective culture——uncertainty analysis of data from the Luria-Delbrück fluctuation experiment

Whether bacterial drug-resistance is drug-induced or results from rapid propagation of random spontaneous mutations in the flora prior to exposure, remains a long-term key issue concerned and debated in both genetics and medicinal fields. In a pio-neering study, Luria and Delbruck exposed E. coli to T1 phage, to investigate whether the number of resistant colonies fol- lowed the Poisson distribution. They deduced that the development of resistant colonies is independent of phage presence. Similar results have since been obtained on solid medium containing antibacterial agents. Luria and Delbruck＇s conclusions were long considered a gold standard for analyzing drug resistance mutations. More recently, the concept of adaptive mutation has triggered controversy over this approach. Microbiological observation shows that, following exposure to drugs of various concentrations, drug-resistant cells emerge and multiply depending on the time course, and show a process function, incon-sistent with the definition of Poisson distribution （which assumes not only that resistance is independent of drug quantity but follows no specific time course）. At the same time, since cells tend to aggregate after division rather than separating, colonies growing on drug plates arise from the multiplication of resistant bacteria cells of various initial population sizes. Thus, statisti-cal analysis based on equivalence of initial populations will yield erroneous results. In this paper, 310 data from the Lu- ria-DelbNck fluctuation experiment were reanalyzed from this perspective. In most cases, a high-end abnormal value, resulting from the non-synchronous variation of the two above-mentioned time variables, was observed. Therefore, the mean value cannot be regarded as an unbiased expectation estimate. The ratio between mean value and variance was similarly incompara-ble, because two different sampling methods were used. In fact, the Luria-Delbrtick data appear to follow an aggregated, rather than Poisson distribution. In stmnnary, the statistical analysis of Luria and Delbruck is insufficient to describe rules of resistant mutant development and multiplication. Correction of this historical misunderstanding will enable new insight into bacterial resistance mechanisms.